Generally, scales on a surface of a steel plate are removed by polishing the surface of the steel plate. The polishing of the surface is an important process for post-machining of a steel plate. For example, when a polished steel plate is bent to form a tank wall of an oil tank, a flaw on a surface of a supplied steel plate remaining on a polished surface may cause the steel plate to be broken by bending stress. Thus, the polishing of the surface needs to be finished without any flaw remaining on the polished surface. Generally, coating is applied on the polished surface to protect the surface, and the polished surface needs to have surface roughness suitable for coating.
As means for forming such a polished surface, a rotating polishing tool has been adopted in which a plurality of laminated disk-shaped abrasive cloth/paper sheets constitute a cylindrical polishing member, the polishing member is rotated around a central axis thereof to polish a polished surface with a peripheral surface of the polishing member, that is, a peripheral edge of each abrasive cloth/paper sheet.
When the polishing member including the plurality of flat abrasive cloth/paper sheets simply laminated is adopted, the polished surface is microscopically polished only by a peripheral edge of each abrasive cloth/paper sheet and not polished by portions between the abrasive cloth/paper sheets. Thus, the peripheral edge of each abrasive cloth/paper sheet comes into contact with the polished surface to produce a plurality of streak-like irregularities on a finished polished surface.
On the other hand, Patent Document 1 discloses a rotating polishing tool in which peripheral edges of abrasive cloth/paper sheets are formed into a serpentine shape to prevent production of streak-like irregularities, thereby finishing a polished surface with desired surface roughness.
FIG. 8 shows the rotating polishing tool disclosed in Patent Document 1. In the rotating polishing tool 12, a plurality of laminated abrasive cloth/paper sheets 7 are pressingly held by an inner metal fitting 8, the inner metal fitting 8 is bent to form a polishing unit 9 having a serpentine peripheral edge, and a plurality of polishing units 9 are laminated to constitute a cylindrical polishing member 11. While rotating the polishing member 11, this configuration allows the peripheral edges of the abrasive cloth/paper sheets 7 to move reciprocatively in the direction of a central axis to bring the peripheral edges of the abrasive cloth/paper sheets 7 into contact with the entire polished surface.
[Patent Document 1] Japanese Patent Laid-Open No. 2004-1145 (paragraphs 0006, 0015, and 0016, and FIG. 2)